Low profile image combiner for near-eye displays

ABSTRACT

An image combiner, also referred to as a combiner optic, of a near-eye display system or the like transmits enough light so a user can see remote objects in a “world view”, while also reflecting enough light so the user can simultaneously see a projected image in a “projected” (augmented) view. The disclosed image combiners use two partial reflectors configured to form a wedged reflective cavity. In the display system, light from an imaging device follows a path to the user&#39;s eye that includes three reflections in the wedged cavity. By using this capability of the wedged cavity, the combiner optic can have a substantially reduced thickness, and lower profile, than a combiner optic that uses only one partial reflector and only one reflection in the optical path.

FIELD OF THE INVENTION

This invention relates generally to lenses and related opticalcomponents, with particular application to optical components thatinclude a partially reflective element to allow simultaneous viewing ofremote objects and a projected image. The invention also relates toassociated articles, systems, and methods.

BACKGROUND

Optical beamsplitters are known. Some beamsplitters are made bycementing two prisms together with a reflective film in between. Seee.g. U.S. Pat. No. 7,329,006 (Aastuen et al.) Lenses are also known.Known lenses include compound lenses in which two or more simple lensesare cemented together. U.S. Pat. No. 5,654,827 (Reichert) discusseslenses in which the lens is divided into two parts by a beamsplitter.

Head-Up Displays or Head-Mounted Displays (collectively referred toherein as HUDs) can project an image that fills all or part of a user'sfield of view. Some HUDs use a combiner optic that integrates theprojected image with the usual image of the external environment. Insome cases, the HUD is a Near-Eye Display (NED), which may have a formfactor similar to that of eyeglasses. See e.g. U.S. Pat. No. 6,353,503(Spitzer et al.).

BRIEF SUMMARY

In near-eye displays and the like, the display system uses at least onecombiner optic, such as a combiner lens, that optically combines a worldview with an augmented (projected) view by superimposing one on theother. In the world view, the user sees distant objects through thecombiner optic. In the augmented view, the user sees an image producedby a small projector and reflected into the user's eye by the combineroptic. The system preferably combines the two views with high qualityoptical performance and in a robust package. Furthermore, it isdesirable for the glasses to be lightweight and aesthetically pleasing.The combiner optic can play a significant role not only in the opticalperformance but also the aesthetics and the weight of the displaysystem.

We have developed a new family of combiner optics, such as combinerlenses, that can provide the two superimposed views in a component sizewhose axial dimension (thickness) can be made quite small. The reducedthickness can be used to reduce the volume and thus the weight of thecombiner optic, as well as enhance system aesthetics by providing athin, modern, “low profile” design. The reduced thickness capability ismade possible by certain optical design features of the combiner optic.In brief, the combiner optic uses two partial reflectors that form awedged reflective cavity. Imaging light that produces the projected(augmented) view follows a path from the imaging device to the user'seye, and the partial reflectors are configured so that this light pathincludes three reflections in the wedged reflective cavity. By employingthe multiple reflections in the reflective cavity, the partialreflectors can be oriented at a smaller tilt angle, i.e., more nearlyperpendicular to the longitudinal or optical axis of the combiner optic,compared to the tilt angle that would be needed for a single-reflectionbeamsplitter, which makes possible the thinner product configuration.The less tilted design feature of the disclosed combiner optics is alsobeneficial for wide angle viewing, both for the world view and for theprojected view.

We therefore describe herein, among other things, display systems thatpermit simultaneous viewing of remote objects and a projected image, thesystems including a combiner optic and an imaging device. The combineroptic has a proximal end and a distal end, the proximal end beingsuitable for placement near a user's eye. The imaging device is disposedto direct imaging light towards the proximal end of the combiner optic.The combiner optic includes first and second partial reflectors thatform a wedged reflective cavity, and the imaging light follows a lightpath to the user's eye that includes three reflections in the wedgedreflective cavity.

The first partial reflector may be or include a reflective polarizer.The reflective polarizer may be disposed at or near the proximal end ofthe combiner optic, such that the imaging light propagating along thelight path encounters the reflective polarizer before encountering thesecond partial reflector. The reflective polarizer may be or include acircular reflective polarizer. The reflective polarizer may be orinclude a linear reflective polarizer, and the combiner optic mayfurther include a retarder layer disposed between the first and secondpartial reflectors. The retarder layer may have a retardance ofsubstantially λ/4. The three reflections in the reflective cavity mayinclude a first reflection at the reflective polarizer and a first andsecond reflection at the second partial reflector. The retarder layermay have a fast axis and the reflective polarizer may have a pass axis,and the fast axis may be oriented relative to the pass axis so that thefirst reflection at the reflective polarizer occurs with little or notransmission of the imaging light through the reflective polarizer.

The combiner optic may include distinct first and second lenses, and thefirst lens may attach to the second lens through the second partialreflector. The first lens may have a first curved surface, and thesecond lens may have a second curved surface shaped to match the firstcurved surface.

The second partial reflector may be or include a notched reflector. Overa wavelength range from 400-700 nm, the notched reflector may include atleast one distinct reflection band whose full width at half maximum(FWHM) is less than 100 nanometers. The second partial reflector mayhave a reflectivity at normal incidence that is substantiallyinsensitive to polarization state. Over a wavelength range from 400-700nm, the second partial reflector may have no distinct reflection bandwhose full width at half maximum (FWHM) is less than 100 nanometers. Thefirst partial reflector may have an average reflectivity for the imaginglight in a range from 25% to 75%, and the second partial reflector mayhave an average reflectivity for the imaging light in a range from 25%to 75%.

The reflective polarizer may define a pass state and a block state ofpolarization, and the block state of the reflective polarizer mayprovide a notched reflection spectrum, and the imaging light maycomprise one or more distinct spectral output peaks corresponding to thenotched reflection spectrum. Furthermore, the second partial reflectormay be or include a notched reflector having a second notched reflectionspectrum corresponding to the notched reflection spectrum of the blockstate of the reflective polarizer.

We also describe combiner optics that have a proximal end and a distalend, such combiner optics including a first lens at or near the proximalend and a second lens at or near the distal end. First and secondpartial reflectors may be disposed on opposed ends of the first lens,the first partial reflector being attached to a first surface of thefirst lens, and the second partial reflector being sandwiched betweenthe first and second lenses. The first and second partial reflectors mayhave sufficient light transmission to permit viewing of remote objectsthrough the combiner optic, and the first and second partial reflectorsmay form a wedged reflective cavity.

The first partial reflector may be or include a reflective polarizer.The first partial reflector may be or include a linear reflectivepolarizer, and the combiner optic may also include a retarder layerdisposed between the first and second partial reflectors. The first andsecond partial reflectors may have reflectivities tailored such thatimaging light directed at the proximal end provides a viewable image toan eye disposed near the proximal end via a light path that includesthree reflections in the wedged reflective cavity.

We also disclose optics (optical elements) that redirect light from asource to a detector. The optic includes a reflective polarizer and areflector arranged to form a wedged reflective cavity. The optic alsoincludes a retarder layer between the reflective polarizer and thereflector. The retarder layer is oriented relative to the reflectivepolarizer such that light that enters the wedged reflective cavitythrough the reflective polarizer exits the wedged reflective cavitythrough the reflective polarizer after three reflections in the wedgedreflective cavity.

The reflective polarizer may be a broad band polarizer that operatesover most or all of a visible wavelength spectrum, or the reflectivepolarizer may instead be or include a notched reflector. In either case,the reflective polarizer may have a reflectivity for at least some lightin a block state of polarization of over 50%, or over 70%, or over 90%,or over 99%. The retarder layer may have a retardance of substantiallyλ/4. The reflector may be a partial reflector with sufficient lighttransmission to permit optical detection of remote objects through thewedged reflective cavity and through the optic, such that the optic is acombiner optic. Alternatively, the optic may have insufficient lighttransmission to permit optical detection of remote objects through thewedged reflective cavity or through the optic, such that the optic isnot a combiner optic. Systems that incorporate such optics are alsodisclosed. The systems may include an imaging device that directsimaging light towards the reflective polarizer of the optic. The systemsmay also or alternatively include a detector disposed to receive thelight that exits the wedged reflective cavity through the reflectivepolarizer. In some cases the detector may be a person's eye, or it mayinstead be or include an electronic detector.

Other aspects of the invention can be found in the appended claims andthe detailed description that follows.

Related methods, systems, and articles are also discussed.

These and other aspects of the present application will be apparent fromthe detailed description below. In no event, however, should the abovesummaries be construed as limitations on the claimed subject matter,which subject matter is defined solely by the attached claims, as may beamended during prosecution.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic top view of a near-eye display system, in the formof eyewear, that incorporates a left and right combiner optic asdescribed herein, and FIGS. 1A and 1B are schematic views showing howthis eyewear allows the user to see a world view and a projected viewrespectively;

FIG. 2A is a schematic side or sectional view of a display system inwhich the combiner optic uses only one partial reflector, and FIG. 2Bshows that the light path from the imaging device to the eye for thissystem has only one reflection at the combiner;

FIG. 3A is a schematic side or sectional view of a display system inwhich the combiner optic uses two partial reflectors configured as awedged reflective cavity, and FIG. 3B shows that the light path from theimaging device to the eye for this system has three reflections in thereflective cavity;

FIG. 4 is an enlarged schematic view of a combiner optic having twopartial reflectors configured as a wedged cavity, with light rays drawnto show a portion of the light path from the imaging device to the eyeas well as reflections and refractions of the imaging light that producestray light beams;

FIGS. 5 and 6 are enlarged schematic views of additional combiner opticsthat have two partial reflectors configured as a wedged cavity, thesecombiner optics also including additional elements to reduce stray lightbeams;

FIG. 7 is a graph of the measured spectral reflectivity of a partialreflector that was combined with another partial reflector to make acombiner optic that was made and tested;

FIG. 8 is a photograph of the combiner optic that was made and tested,the combiner optic placed on a printed surface so that transmitted andreflected images can be seen; and

FIG. 9 is a photograph of the combiner optic being illuminated withpolarized imaging light and reflecting the imaging light onto a surface.

In the figures, like reference numerals designate like elements.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

As mentioned above, we have developed combiner optics whose axialdimension or thickness can, if desired, be made smaller than that of aconventional combiner optic due to the incorporation of two partialreflectors that are tilted relative to each other to form a wedgedreflective cavity. In forming the projected view, light from an imagingdevice in the display system follows a path to the user's eye thatincludes three reflections in the wedged reflective cavity.

Turning to FIG. 1, we see there a schematic view of a display system 110that allows a user to simultaneously perceive a world view and aprojected view. The system 110 is shown in the context of a Cartesianx-y-z coordinate system for ease of description. The world view may beassociated with real objects such as remote object 104. The projectedview is produced by one or both of a left imaging device 130 and a rightimaging device 150, and may be superimposed on the world view. Theprojected view is represented in the figure by a virtual object 105which is formed by the projected light. In some cases, two differentprojected views, with two or more different associated virtual objects,may be provided, e.g. a left projected view provided by the left imagingdevice 130 and a right projected view provided by the right imagingdevice 150. If distinct left and right projected views are provided,they may be left and right stereoscopic views of one or more virtualobjects, thus providing a 3-dimensional appearance or illusion of suchobject(s) to the user. Alternatively, the left and right projected viewsmay instead be views of different unrelated virtual objects. In stillother cases, one of the imaging devices 130, 150 may be omitted, suchthat the display system 110 includes only one imaging device, andprovides only one projected view.

The disclosed display systems may be made in any suitable style orformat, such as eyewear (e.g. eyeglasses) or headwear (e.g. hats,helmets, or visors), so long as at least one combiner optic and itsassociated imaging device is held in place or otherwise positioned orsuspended near an eye of the user. The display system 110 of FIG. 1 isillustrated as eyewear, and as such it includes a suitable frame 112that may be supported by the ears and nose of the user. The frame 112holds a left combiner optic 120 and a right combiner optic 140 in placenext to a left eye 102 and a right eye 103, respectively, of the user.The frame also holds a left imaging device 130 and a right imagingdevice 150 near, and at an appropriate orientation angle relative to,their respective combiner optics 120, 140.

The combiner optic 120 has opposed first and second optical surfaces 120a, 120 b, which are typically outermost surfaces exposed to air. Thefirst optical surface 120 a is at a proximal end of the optic 120,suitable for placement near the user's eye 102. The second opticalsurface 120 b is at a distal end of the optic 120, facing away from theuser and outward toward any remote object(s) that may be present. Acircumferential side surface 120 c connects the first optical surface120 a with the second optical surface 120 b. The combiner optictypically includes two or more distinct optical bodies such as lenses orprisms that mate with each other and are bonded or otherwise attached oraffixed together so that the combiner optic is in the form of a singleoptical module or package. The combiner optic 120 is shown as being madeof one optical body 122 at the proximal end of the optic and anotheroptical body 124 at the distal end of the optic. The optical surfaces ofthese optical bodies may be planar, non-planar (e.g., curved), orcombinations of planar and non-planar, such as in the case of bodies 122and 124, each of which has one planar optical surface and one curvedoptical surface.

The optical body 122, the optical body 124, and other optical bodiesdisclosed herein may be considered to be a lens if at least one of itsoptical surfaces is curved, e.g., convex or concave, rather than beingflat or planar. The curvature may be spherical, i.e., it may have aconstant radius of curvature over substantially the entire opticalsurface, or it may be aspherical, with a radius of curvature thatchanges over the optical surface, usually in a gradual and continuousfashion. The curvature provides the optical body with a non-zero opticalpower, e.g. a positive optical power in the case of a converging lens ora negative optical power in the case of a diverging lens, unless bothoptical surfaces have the same curvature, in which case the lens mayhave a zero optical power and may be neither converging nor diverging.Also, the curvature of the optical surface of a body may reside in twoorthogonal cross-sectional planes, e.g. the x-z plane and the y-z planeof FIG. 1, or it may reside in only one of two orthogonalcross-sectional planes, e.g., it may reside in the x-z plane but not they-z plane.

An optical body whose opposed optical surfaces are both planar, buttilted or skewed relative to each other, may be referred to herein as aprism rather than a lens. See e.g. FIG. 3.

A given combiner optic may include optical bodies that are lenses and/orprisms. Depending on whether the optical surfaces of the optical bodiesare planar or curved, and depending on other factors such as therefractive indices of the optical bodies, the combiner optic 120 mayhave a non-zero optical power, e.g. it may have a net converging effector a net diverging effect on light that passes through it, or it mayhave a zero or substantially zero optical power. Note also that theoptical power provided by the combiner optic may be, and typically is,different for the world view compared to the projected view, due to thedifferent light paths used by these two views. In the case of combineroptic 120, if the optical bodies 122, 124 have the same or similarrefractive index, and the optical surfaces 120 a, 120 b aresubstantially planar, the optic 120 may have substantially zero opticalpower for the world view, but, if the partial reflector 128 is curved asshown, it may have a significant non-zero optical power for theprojected view.

Each combiner optic may define a longitudinal or optical axis. This axismay be defined to coincide with the optical axis of the eye it isdesigned to work with. Thus, in FIG. 1, the longitudinal axis 121 ofcombiner optic 120 also coincides with the optical axis of the user'sleft eye 102 when the display system 110 is properly positioned on ornear the user's head, and the longitudinal axis 141 of combiner optic140 coincides with the optical axis of the user's right eye 103. In manycases, the longitudinal axis of a given combiner optic also passesthrough the geometrical centers of at least the optical surfaces at theproximal and distal ends of the optic, e.g., optical surfaces 120 a, 120b of combiner optic 120. Although the longitudinal axis may be an axisof symmetry with respect to one or some optical surfaces of the combineroptic, such as the opposed optical surfaces at the proximal and distalends of the optic, it may not be—and in many cases is not—an axis ofsymmetry of other optical surfaces, particularly an optical surface thatis embedded in the combiner optic and associated with one of the twopartial reflectors in the combiner optic.

In this regard, the combiner optic 120 of FIG. 1 includes a partialreflector 126 and a partial reflector 128. The partial reflector 128 isembedded in the combiner optic 120 and is tilted and curved in such away that it is not symmetric with respect to the longitudinal axis 121of the optic 120. More aspects and features of the partial reflectorsare discussed further below. One or both of the two partial reflectorsin the combiner optic are preferably tilted relative to the longitudinalaxis, and may also be curved, in such a way as to define a wedgedreflective cavity. The cavity is wedged because it is designed to workwith the imaging device, which is separated from, and off to one sideof, the user's eye, and thus also displaced from the longitudinal axisof the optic. In the case of combiner optic 120, the partial reflectors126, 128 form a wedged reflective cavity 129. The partial reflectors126, 128 and the cavity 129 are configured so that imaging light of theprojected view follows a path from the imaging device 130 to the user'sleft eye 102 that includes three reflections in the cavity 129.

The various parts and features of the left combiner optic 120 have nowbeen discussed. The reader will understand that the right combiner optic140 may have the same or substantially similar design as the left optic120, except that it may have a mirror image symmetry relative to theoptic 120, as shown in FIG. 1. Thus, the right combiner optic 140 hasopposed first and second optical surfaces 140 a, 140 b at proximal anddistal ends of the optic 140, a circumferential side surface 140 c, anoptical body 142 at the proximal end and another optical body 144 at thedistal end of the optic 140, a longitudinal or optical axis 141, andpartial reflectors 146, 148 that form a wedged reflective cavity 149,and all of these elements may be the same as or similar to theirrespective counterparts in the right combiner optic 120.

FIGS. 1A and 1B are schematic views of the display system of FIG. 1 inoperation. FIG. 1A shows how light that produces the world view ishandled by the system. FIG. 1B shows how light that produces theprojected view is handled by the system. In these figures, likereference numbers refer to like elements from FIG. 1, and theirdescriptions will not be repeated here.

In FIG. 1A, light 106 from one or more remote objects propagates fromthe object(s) to the user of the system 110. The light 106 is typicallyvisible light, but may also be or include non-visible wavelengths suchas ultraviolet and/or near infrared. The light 106 is also typicallyunpolarized, but in some cases it may be weakly or even stronglypolarized. In a simple case, the light may be unpolarized, broadbandwhite light, e.g., ambient sunlight, daylight, or office lightingreflected off of a physical object. The light 106 encounters theoutermost optical surfaces 120 b, 140 b of the combiner optics 120, 140,whereupon the light 106 enters the respective combiner optics byrefraction. Unless an antireflection coating is provided at thoseoutermost optical surfaces, some reflection will also occur at thosesurfaces in accordance with the well-known Fresnel equations for asimple air/dielectric interface. In this regard, the optical bodies thatmake up the combiner optics, such as optical bodies 122 and 124 of optic120 and optical bodies 142 and 144 of optic 140, may be made of anysuitable light-transmissive optical material, for example, an opticallyclear polymer such as a polycarbonate, an acrylate such aspolymethylmethacrylate (PMMA), a cyclic polyolefin copolymer and/or acyclic polyolefin polymer, or a silicone, or an optical glass or ceramicsuch as a soda lime glass, a borosilicate glass, silica, or sapphire.All or most of these materials are dielectrics. Typically, the opticalbodies of a given combiner optic, such as bodies 122 and 124 of combineroptic 120, are composed of the same or similar optical material, andhave the same or similar refractive index. But in some cases, the bodies122, 124 may be composed of substantially different optical materials,and may have substantially different refractive indices, orsubstantially the same refractive indices with some materialcombinations. The refractive index of each body 122, 124 is typicallyisotropic rather than birefringent. Even though a simple air/dielectricinterface reflects some light and transmits the remainder, such aninterface is not considered to be a “partial reflector” for purposes ofthis application. The amount of light reflected at such an interface isalso typically quite small, e.g., less than 8%, or less than 6%, or lessthan 5% for light that is incident at normal or near-normal incidenceangles.

Referring now for convenience to the left combiner optic 120, the light106 that enters the combiner optic propagates through the optical body124 (see FIG. 1) until it encounters the partial reflector 128. In thisembodiment, the partial reflector 128 is assumed to be sandwichedbetween matching curved surfaces of the bodies 122, 124. Here, dependingon the characteristics of the light 106 (such as wavelength,polarization, incidence angle) and the characteristics of the partialreflector 128, a portion of the light 106 may be reflected, and theremainder transmitted through the partial reflector 128 into the opticalbody 122 (see FIG. 1). The portion of the light 106 that is reflected atthe partial reflector 128 may be small or minimal, e.g., less than 10%,or less than 5%, for example if the partial reflector 128 is a(spectrally) notched reflector and a substantial portion of the light106 is at wavelengths that avoid the reflection band(s) of the notchedreflector, or if the partial reflector is a reflective polarizer and asubstantial portion of the light 106 has a polarization orthogonal tothe polarization reflected by the reflective polarizer. Alternatively, amore significant portion of the light 106 may be reflected at thepartial reflector 128, e.g., up to 20%, or up to 30%, or up to 40%. Inmany cases, the optical absorption of the partial reflector 128 may besmall or negligible, such that the portion of the light 106 that istransmitted by the partial reflector 128 substantially or approximatelyequals 100% minus the amount of the light 106 that is reflected by thepartial reflector 128. In some cases, however, such as where the partialreflector 128 is or includes a metal vapor coat, the absorption may bemore significant, such that the sum of reflectivity and transmission isless than 100%.

The portion of the light 106 that is transmitted by the partialreflector 128 propagates through the optical body 122 (see FIG. 1) tothe partial reflector 126. In this embodiment, the partial reflector 126is assumed to be formed on, adhered to, or otherwise applied to theouter optical surface of the optical body 122. At the partial reflector126, depending on characteristics of the light 106 and thecharacteristics of the partial reflector 126 (see the discussion aboverelating to the partial reflector 128), a portion of the light 106 maybe reflected, and the remainder transmitted through the partialreflector 126, out of the combiner optic 120, and onward to the user'seye 102.

FIG. 1B shows how the display system 110 operates in providing aprojected view to the user. In the description that follows, we willconcentrate on the operation of the left half of the system 110, withthe understanding that the right half, which includes the imaging device150 and the right combiner optic 140, may operate in substantially thesame or similar way.

The imaging device 130 may be or comprise an OLED display, atransmissive liquid crystal display, a reflective LC display (such as,for example, a Liquid Crystal on Silicon (LCoS) display), or a scannedlaser device. In any case, the device 130 emits imaging light 132 whichcan be perceived by the user as a virtual image, after reflection by thecombiner optic. The imaging light 132 may be ordinary unpolarized whitelight, or it may have specific properties, e.g., spectral and/orpolarization properties, that are tailored to match or substantiallymatch optical characteristics of one or both of the partial reflectors126, 128 to enhance system efficiency, e.g., so that one or both of thepartial reflectors 126, 128 provide a higher reflectivity for theimaging light 132, while also providing a high transmission of lightfrom remote objects. Thus, the device 130 may emit polarized light, andone or both of the partial reflectors 126, 128 may then be tailored tohave a higher reflectivity for that polarization state and a lowerreflectivity (and higher transmission) for light of the orthogonalpolarization state. Alternatively or in addition, the device 130 mayemit imaging light selectively in one or more narrow bands (e.g., it mayemit light in only one narrow band, such as in the red, green, or blueregion of the spectrum, or it may emit light in two or three such narrowbands that do not substantially overlap), and the partial reflector(s)may then be tailored to have a high reflectivity only in the narrow bandor bands of the imaging light 132. The foregoing may be restated bynoting that one or each of the partial reflectors may, in someembodiments of the display system, be tailored to have a higherreflectivity, and lower transmission, for the imaging light 132 than forordinary ambient light (e.g., unpolarized, broadband white light) whichmay typically characterize the light emitted by remote objects.

Upon leaving the imaging device 130, the imaging light 132 follows apath that involves an interaction with the combiner optic 120 and endsat the retina of the user's eye 102, the interaction with the optic 120including multiple reflections in the wedged reflective cavity 129formed by the partial reflectors 126, 128. The imaging light 132encounters the outermost optical surface 120 a of the combiner optic 120at its proximal end, at which (in the embodiment of FIG. 1) the partialreflector 126 is located. Some of the light 132 is reflected here, and aremaining portion is transmitted by the partial reflector 126 and entersthe wedged reflective cavity 129 by refraction. The cavity 129 in thiscase substantially corresponds to the optical body 122. Thetransmitted/refracted portion of the imaging light 132 then propagateswithin the reflective cavity 129 and optical body 122, where a portionof it is reflected first by the partial reflector 128, then by thepartial reflector 126, and again by the partial reflector 128. After thethird reflection in the cavity 129 (which is the second reflection atthe partial reflector 128), the path of the light 132 leads to thepartial reflector 126, where a portion of the light is reflected and aportion of the light is transmitted. The light 132 that is transmittedat this point exits the combiner optic 120 and travels onward to theuser's eye 102 along the longitudinal axis 121. The ray of imaging light132 shown schematically in the figure is but one of a bundle of raysemitted by the imaging device 130, each of which follow paths withsimilar characteristics, and in particular with three reflections in thereflective cavity 129, the collection of these rays combining to presenta projected image to the user which may be superimposed on the user'sworld view.

FIGS. 2A-B and 3A-B schematically illustrate an advantage provided byoptical display systems that utilize a wedged reflective cavity andmultiple reflections in the optical path of the projected image,compared to systems that use only one partial reflector, and only onereflection. FIGS. 2A-B are provided for comparison or reference, andrelate to a display system in which the combiner optic has only onepartial reflector and uses only one reflection. FIGS. 3A-B relate to adisplay system in which the combiner optic has two partial reflectorsarranged to form a wedged reflective cavity. Briefly, the multiplereflections provided by the wedged reflective cavity (FIG. 3A) allow thepartial reflector to be oriented at a smaller tilt angle, i.e., morenearly perpendicular to the longitudinal or optical axis of the combineroptic, than the partial reflector in the comparison system (FIG. 2A).The smaller tilt angle of the partial reflector in turn allows thecombiner optic of FIG. 3A to have a smaller longitudinal dimension,i.e., it can be made thinner, compared to the combiner optic of FIG. 2A.

In FIG. 2A, a display system 210 includes a combiner optic 220 which, incombination with an imaging device 230, provide a projected image to auser's eye 202. Similarly, in FIG. 3A, a display system 310 includes acombiner optic 320 which, in combination with an imaging device 330,provide a projected image to a user's eye 302. The combiner optics inthese figures may have respective longitudinal or optical axes (axis 221in FIG. 2A, axis 321 in FIG. 3A) which in both cases coincide with theoptical axis of the user's eye, parallel to the z-axis. The imagingdevice in each case is offset from the user's eye, and oriented in adirection characterized by an incidence angle θinc relative to thelongitudinal axis of the respective combiner optic. For ease ofcomparison, the orientation angle θinc is the same in FIGS. 2A and 3A.

In FIG. 2A, imaging light 232 is emitted from the imaging device 230 atthe angle θinc toward the combiner optic 220. The imaging light 232encounters an outer optical surface 220 a of the optic 220. The outersurface 220 a is assumed to be a simple air/dielectric interface, and isassumed to be perpendicular to the longitudinal axis 221. As such, asmall portion of the light 232 is reflected as stray light, and theremainder is transmitted and refracted into an optical body 222 such asa prism (or lens). The optical body 222 is part of the combiner optic220 of FIG. 2A. The transmitted, refracted light 232 propagates throughthe optical body 222 and is reflected at a distal optical surface of thebody 222, at which a partial reflector 228 is provided. The partialreflector 228 and optical surface are tilted at an angle θtilt relativeto a reference axis or plane 205 that is perpendicular to thelongitudinal axis 221 of the combiner optic. The tilt angle θtilt isselected so that the portion of the light 232 that is reflected at thepartial reflector 228 is directed parallel to the longitudinal axis 221to the user's eye 202. FIG. 2B illustrates schematically the light path235 that is followed by the imaging light 232 in the system of FIG. 2A.The imaging light 232 exits the imaging device 230 at point a, isrefracted at the surface 220 a at point b, is reflected at the partialreflector 228 at point c, emerges from the surface 220 a of the combineroptic at point d, and reaches the user's eye at point e. Any reflectionsor refractions that may occur within the imaging device 230 are ignored,and are not included in our analysis of the light path 235.

In FIG. 3A, imaging light 332 is emitted from the imaging device 330 atthe angle θinc toward the combiner optic 320. The angle θinc is drawn tobe the same as the angle θinc in FIG. 2A. Referring still to FIG. 3A,the imaging light 332 encounters an outer optical surface 320 a of theoptic 320. The outer surface 320 a is assumed to coincide with a partialreflector 326, and is assumed to be perpendicular to the longitudinalaxis 321. As such, some of the light 332 is reflected as stray light,and the remainder is transmitted and refracted into an optical body 322such as a prism (or lens). The optical body 322 is part of the combineroptic 320 of FIG. 3A, and it is assumed to have the same refractiveindex as the optical body 222 of FIG. 2A, thus producing the same angleof refraction for the light that is refracted into the outer opticalsurface of the combiner optic. The transmitted and refracted light 332propagates through the optical body 322 and is reflected at a distaloptical surface of the body 322, at which another partial reflector 328is provided. The partial reflector 328 and optical surface are tilted atan angle θtilt relative to a reference axis or plane 305 that isperpendicular to the longitudinal axis 321 of the combiner optic. Thepartial reflectors 328, 326 thus form a wedged reflective cavity 329.The light 332 reflected at the partial reflector 328 travels to theother partial reflector 326, where a portion of it is reflected back tothe partial reflector 328, and a portion of that light travels back tothe partial reflector 326, where some of that light is transmitted andexits the combiner optic 320. The tilt angle θtilt of the partialreflector 328 is selected so that the portion of the light 332 thatexits the combiner optic after three reflections in the cavity 329 isdirected parallel to the longitudinal axis 221 to the user's eye 202. Ascan be seen by comparison of the figures, the tilt angle θtilt of FIG.3A is substantially smaller than that of FIG. 2A. This is because of thethree reflections that are experienced in the wedged reflective cavityof combiner optic 320.

In this regard, FIG. 3B illustrates schematically the light path 335that is followed by the imaging light 332 in the system of FIG. 3A. Theimaging light 332 exits the imaging device 330 at point a, is refractedat the partial reflector 326 (and optical surface 320 a) at point b, isreflected at the partial reflector 328 at point c, is reflected at thepartial reflector 326 at point d, is reflected again at the partialreflector 328 at point e, emerges from the partial reflector 326 (andoptical surface 320 a) at point f, and reaches the user's eye at pointg. Any reflections or refractions that may occur within the imagingdevice 330 are ignored, and are not included in our analysis of thelight path 335.

FIGS. 4, 5, and 6 illustrate in more detail various combiner opticembodiments, each of which includes two partial reflectors arranged toform a wedged reflective cavity. In some of these embodiments, thepartial reflectors and other elements of the system are tailored toreduce or eliminate one or more stray light beams.

In FIG. 4, a combiner optic 420 is of the type that can be used in thedisclosed display systems. The optic 420 has opposed first and secondoptical surfaces 420 a, 420 b. The optical surface 420 a is at aproximal end of the optic 420, suitable for placement near a user's eye.The optical surface 420 b is at a distal end of the optic 420. Acircumferential side surface 420 c connects the first and second opticalsurfaces 420 a, 420 b. The combiner optic 420 includes distinct opticalbodies (lenses) 422, 424, whose curved optical surfaces substantiallymate with each other and which are bonded or otherwise attached oraffixed together, but with a partial reflector disposed therebetween.The combiner optic 420 defines a longitudinal or optical axis 421. Thisaxis 421 may coincide with the optical axis of the user's eye when thedisplay system, of which the combiner optic 420 is a part, is properlypositioned. The axis 421 may also be perpendicular to the opticalsurfaces 420 a, 420 b, which may be planar and parallel to each other.The combiner optic 420 includes a partial reflector 426 and a partialreflector 428. The partial reflector 428 is embedded in the combineroptic 420, sandwiched between the optical bodies 422, 424, and tiltedand curved in such a way that it is not symmetric with respect to thelongitudinal axis 421. The partial reflector 428 may also have aterminus that extends completely around the circumferential side surface420 c, see terminus 428 t 1, 428 t 2. The partial reflector 426 may beattached to, applied to, or formed on the optical surface of the body422 at the proximal end of the optic 420. The partial reflector 426, andthe optical surface it is attached to, may be planar and orthogonal tothe longitudinal axis 421 as shown, or they may be tilted (notorthogonal) relative to the longitudinal axis, and/or they may benon-planar, e.g., having a concave or convex curvature. In any case, oneor both of the partial reflectors 426, 428 are tilted relative to thelongitudinal axis so that the reflective cavity 429 has a wedgedconfiguration. The partial reflectors 426, 428 and the cavity 429 aredesigned so that imaging light of the projected view follows a path fromthe imaging device to the user's eye that includes three reflections inthe cavity 429.

In general, a variety of different films, layers, and similar elementscan be used for the partial reflectors that form the reflective cavityin the disclosed display systems. For practical reasons of size, space,and/or weight, each partial reflector preferably has a thin form factor,such as in the case of a single layer film or multiple layer film orfilm combination, the overall thickness of which may be e.g. less than 1mm, or less than 0.5 mm, or less than 0.1 mm, rather than a bulk opticalcomponent. A given partial reflector provides more reflectivity thanthat of a simple dielectric/air interface, but not so much that thepartial reflector's transmission is so low that (in combination with theother partial reflector and other components of the combiner optic) theuser can no longer see remote objects through the combiner optic. Forexample, one or both partial reflectors may have an average reflectivityfor visible light, and/or for the imaging light that is emitted by theimaging device of the display system, in a range from 25% to 75%.Similarly, one or both partial reflectors may have an averagetransmission for visible light, and/or for the imaging light that isemitted by the imaging device of the display system, in a range from 25%to 75%. In many cases, the partial reflector has a small or negligibleabsorption over the wavelength range of interest, such that the sum ofthe reflectivity and the transmission of the partial reflector equals100% at any given wavelength, polarization, and incidence angle. Inother cases, absorption of a partial reflector may be more significant,such that the sum of reflectivity and transmission is substantially lessthan 100% over some or all of the wavelength range of interest.

In some cases, the transmission and reflectivity of a given partialreflector may exhibit little or no variation as a function of theoptical wavelength, and also little or no variation as a function ofpolarization (for normal and near-normal angles of incidence). Forexample, a simple, thin vapor coat of aluminum, silver, or othersuitable metal or material can be applied to a clear film, or directlyto an optical surface of a lens, prism, or other optical body in thecombiner optic, and such a vapor coat may have a reflectivity andtransmission that is constant, or substantially constant, over some orall of the visible wavelength range, and independent, or substantiallyindependent, of polarization state (for light that is incident at normalor near-normal angles). As another example, some multilayer opticalfilms, such as some of those discussed in patent application publicationUS 2010/0165660 (Weber et al.), can be designed to provide a broadreflection band of intermediate reflectivity (i.e., partiallyreflective, with a complimentary, intermediate transmission), with thereflectivity and transmission being substantially constant as a functionof wavelength and as a function of polarization over moderate wavelengthranges and incidence angles. The multilayer optical film may be apolymeric film made of a large number, e.g., tens, hundreds, orthousands, of coextruded polymer layers, or it may be made ofalternating layers of high and low refractive index inorganic materials(e.g., silicon dioxide, titanium dioxide, and other known inorganicoptical materials) that are sequentially evaporated onto a carrier filmor other substrate in a vapor coating chamber.

In other cases, the transmission and reflectivity of a given partialreflector may exhibit significant variation as a function of wavelength,but little or no variation as a function of polarization (for normal andnear-normal angles of incidence). For example, by appropriate control ofthe layer thickness profile of the layers in a polymeric or inorganicmultilayer optical film, one or more distinct reflection bands can beproduced, such that the reflector provides moderate to high reflectivityin such reflection band(s) and much lower reflectivity at otherwavelengths, with a complementary transmission spectrum (i.e., moderateto low transmission at the reflection band(s), and much highertransmission at other wavelengths). Such optical films are referred toherein as (spectrally) notched reflectors, because their reflection ortransmission spectra have a notched or peaked appearance due to thepresence of the distinct, isolated reflection band(s). A given isolatedreflection band can be made quite narrow, e.g., the spectral width ofthe reflection band, as measured by the full-width at half-maximum(FWHM), may be less than 100 nanometers, or less than 75 nanometers.This may be contrasted with partial reflectors that exhibit little or nospectral variability, which may have no distinct reflection band whoseFWHM is less than 100 nanometers.

In other cases, the transmission and reflectivity of a given partialreflector may exhibit little or no variation as a function ofwavelength, but significant variation as a function of polarization (fornormal and near-normal angles of incidence). Examples of this includebroadband reflective polarizers, e.g., reflective polarizers designed tooperate over most or all of the visible wavelength spectrum. Reflectivepolarizers have a high, or relatively high, reflectivity for a blockstate of polarization, and a low reflectivity (and high transmission)for a pass state of polarization. In some cases, such as for certainmultilayer optical films that are oriented by stretching, the block andpass states are linear polarization states that are physicallyorthogonal to each other. In other cases, such as with certaincholesteric optical films, the block and pass states are circular orelliptical polarization states that are mathematically, but notphysically, orthogonal to each other. Regardless of whether thereflective polarizing film is stretched, cholesteric, or otherwise, thelayer thickness profile of such films can be tailored so that thereflectivity of the block state can be broad and relatively constant, orat least slowly varying, as a function of wavelength in the wavelengthrange of interest. A reflective polarizer for circular polarizationstates can also be constructed by combining a linear polarizer with aretarder layer, e.g., a nominally quarter-wave (λ/4) retarder layer,that is suitably oriented.

In still other cases, the transmission and reflectivity of a givenpartial reflector may exhibit significant variation as a function ofboth wavelength and polarization. Examples of this include orientedmultilayer polymer films whose birefringent layers provide thepolarization variability and whose layer thickness profile is tailoredto provide a desired wavelength variability, e.g., one or more isolatedreflection bands. Such a film may for example provide a notchedreflection spectrum for a block state of polarization, and little or noreflection (hence, high transmission) for a pass state of polarization.When used as a partial reflector in the disclosed combiner optics withan imaging device whose emitted imaging light is substantially matchedin wavelength and polarization to the partial reflector (e.g., thepartial reflector may have a notched reflectivity for the blockpolarization, and the imaging device may emit light only in spectralband(s) or peak(s) corresponding to the reflection band(s) of thenotched reflector, the light of the imaging device also being polarizedin the block state), the film can have a surprisingly high averagetransmission for unpolarized ambient white light, but also a highreflectivity for the imaging light emitted by the imaging device.

Combinations of various types of partial reflectors, including thosediscussed above, can be used in the disclosed display systems. The twopartial reflectors that form the wedged reflective cavity may be of thesame type, e.g., they may both exhibit little or no variability inwavelength or polarization, or they may both be notched reflectorsand/or reflective polarizers. Alternatively, the two partial reflectorsmay be of different types. In some cases, the partial reflectors may beselected to increase or maximize system efficiency, e.g., provide hightransmission for ambient light of the world view while also providinghigh reflectivity for imaging light of the projected view. The partialreflectors may also be selected to reduce or eliminate stray light beamsthat may be emitted from the proximal and/or distal ends of the combineroptic.

Turning our attention back to FIG. 4, we can review its operation inconnection with the imaging light provided by the imaging device.Although the imaging device is not shown in FIG. 4, it may be positionedand oriented with respect to the combiner optic as appropriate, e.g. asindicated in FIGS. 1 and 3A. A representative ray 432 of the imaginglight originates from the imaging device, interacts with the combineroptic 420 by reflection, refraction, and transmission, and then entersthe eye of the user along the longitudinal axis 421. The ray 432 is partof a large bundle of rays that make up the imaging light. Exiting theimaging device at a point “a” (not shown in FIG. 4 but see e.g. FIG.3B), the ray 432 follows a path in which it encounters the opticalsurface 420 a, and the partial reflector 426, at point b. The partialreflector 426 may be of a simple design, e.g. a single vapor-coatedlayer of aluminum, or it may be any other suitable partial reflector asdiscussed above. Some of the light 432 is reflected here, and aremaining portion is transmitted by the partial reflector 426 and entersthe wedged reflective cavity 429, and the optical body 422, byrefraction. The transmitted/refracted portion of the light 432, nowlabeled 432 b, then propagates within the reflective cavity 429 andoptical body 422, where a portion of it is reflected first by thepartial reflector 428 at point c (producing ray 432 c 1), then by thepartial reflector 426 at point d (producing ray 432 d 1), and again bythe partial reflector 428 at point e (producing ray 432 e 1). Theencounters at points c, d, and e also in general may produce transmittedrays 432 c 2, 432 d 2, 432 e 2 as shown: the ray 432 d 2 results fromtransmission through the partial reflector 426 and refraction out of thecombiner optic 420; rays 432 c 2 and 432 e 2 propagate through theoptical body 424 to the optical surface 420 b at points g and h,respectively, and are refracted there out of the combiner optic 420 intothe surrounding air to provide rays 432 g, 432 h, respectively. The rays432 d 2, 432 g, and 432 h may be considered extraneous or stray beams ofimaging light. In some applications, such stray light may be entirelyacceptable, and may not have any significant detrimental impact on theoperation of the display system. In other applications, one or more ofthe stray light beams may be undesirable or unacceptable.

Turning again to the light ray whose path begins at the imaging deviceand ends at the eye of the user, and which forms or helps to form theprojected image, the ray 432 e 1 is the result of a second reflection atthe partial reflector 428 and a third reflection in the wedgedreflective cavity 429. The ray 432 e 1 propagates along the longitudinalaxis 421, and part of it is transmitted by the partial reflector 426 atpoint f to produce ray 432 f. The ray 432 f then propagates furtheralong the longitudinal axis 421 until it enters the eye of the user (notshown in FIG. 4) to produce the projected image.

At least some of the stray light can be reduced or eliminated throughjudicious selection of partial reflectors, imaging light, and in somecases one or more other elements of the display system. FIGS. 5 and 6schematically illustrate two such embodiments.

In FIG. 5, a combiner optic 520 suitable for use in the disclosednear-eye display systems is shown. Many of the constituent parts of theoptic 520 may be the same as or similar to corresponding parts of theoptic 420 of FIG. 4. Thus, for example, combiner optic 520 has opposedfirst and second optical surfaces 520 a, 520 b. The optical surface 520a is at a proximal end of the optic 520, suitable for placement near auser's eye. The optical surface 520 b is at a distal end of the optic520. A circumferential side surface 520 c connects the first and secondoptical surfaces 520 a, 520 b. The combiner optic 520 includes distinctoptical bodies (lenses) 522, 524, which may be the same as thecorresponding bodies of FIG. 4. The combiner optic 520 defines alongitudinal or optical axis 521, which may be the same as that of FIG.4. The combiner optic 520 includes a partial reflector 526 and a partialreflector 528. The partial reflector 528 is embedded in the combineroptic 520, sandwiched between the optical bodies 522, 524, and tiltedand curved in such a way that it is not symmetric with respect to thelongitudinal axis 521, and such that it forms a wedged reflective cavity529 with the other partial reflector 526. The partial reflector 528 mayalso have a terminus that extends completely around the circumferentialside surface 520 c, see terminus 528 t 1, 528 t 2. At the proximal endof the optic 520, a partial reflector 526 in combination with a retarderlayer 527 are attached to, applied to, or formed on the optical surfaceof the body 522 as shown. In this case, the partial reflector 526 is alinear reflective polarizer (whether spectrally broadband or spectrallynarrow band (e.g. notched)), and the retarder layer 527 is substantiallya quarter-wave retarder (λ/4) whose in-plane fast axis is orientedrelative to a pertinent in-plane axis of the reflective polarizer (suchas its pass axis or block axis) so that linearly polarized imaging lighttransmitted by the partial reflector 526 is converted by the retarderlayer 527 to circularly polarized imaging light. Stated differently, theretarder layer 527 in combination with the liner reflective polarizer(partial reflector) 526 reflect circularly polarized light of onehandedness (e.g. a “clockwise” or CW circular polarization state) andtransmits circularly polarized light of the other handedness (e.g. a“counter-clockwise” or CCW circular polarization state). The partialreflectors 526, 528 and the cavity 529 are designed so that imaginglight of the projected view follows a path from the imaging device tothe user's eye that includes three reflections in the cavity 529. Theretarder layer 527 and reflective polarizer (partial reflector) 526 areprovided to reduce or eliminate a stray beam of imaging light analogousto ray 432 d 2 of FIG. 4.

We review now the operation of the combiner optic 520 in connection withthe imaging light provided by the imaging device. A representative ray532 of the imaging light originates from the imaging device, interactswith the combiner optic 520, and then enters the user's eye along thelongitudinal axis 521. The ray 532 is part of a large bundle of raysthat make up the imaging light, and this light (including ray 532) maybe polarized or unpolarized, but preferably it is polarized to match thepass axis of the reflective polarizer (partial reflector 526). Afterexiting the imaging device, the ray 532 follows a path in which itencounters the optical surface 520 a, and the partial reflector 526 andretarder layer 527, at point b. The partial reflector 526 is a linearreflective polarizer, as stated above. At point b, a linearly polarizedcomponent of the ray 532 corresponding to the pass state of thereflective polarizer is transmitted by the reflective polarizer 526(thus entering the reflective cavity 529), and the remainder (if any) isreflected. (Note, if the ray 532 is linearly polarized along the passaxis of the reflective polarizer 526, then there will be little or nocomponent of ray 532 in the block state of the reflective polarizer, andthus there may be little or no reflected ray at point b.) Also generallyat point b, as the linearly polarized imaging light transmitted by thereflective polarizer 526 enters the reflective cavity 529, it passesthrough the retarder layer 527, which converts the transmitted/refractedray 532 b to a circularly polarized state, e.g., CW as shown. The ray532 b then propagates across the reflective cavity 529, where a portionof it is reflected first by the partial reflector 528 at point c(producing ray 532 c 1), then by the partial reflector 526 at point d(producing ray 532 d 1), and again by the partial reflector 528 at pointe (producing ray 532 e 1). The encounters at points c and e also ingeneral may produce transmitted rays 532 c 2, 532 e 2 as shown, whichpropagate through the optical body 524 to the optical surface 520 b atpoints g and h, respectively, and are refracted there out of thecombiner optic 520 into the surrounding air to provide stray rays 532 g,532 h, respectively.

Transmitted light is substantially avoided at point d, thus avoiding astray ray analogous to ray 432 d 2 of FIG. 4. This is due to thecombined actions of the reflective polarizer, the retarder layer, andthe other partial reflector. Thus, when the CW circularly polarized ray532 b is reflected at the partial reflector 528, a π phase shifttypically occurs, which converts the CW polarization state to an“orthogonal” CCW polarization state for the reflected ray 532 c 1. Thispolarization state is substantially entirely reflected by the retarderlayer 527/reflective polarizer 526 combination at point d, with littleor no transmitted light. The CCW polarization state is maintained forthe reflected ray 532 d, but reversed again to CW at point e for thereflected ray 532 e 1. With the CW polarization state, the ray 532 e 1,which propagates along the longitudinal axis 521, is highly transmittedat point f by the retarder layer 527/reflective polarizer 526combination, thus producing ray 5321. The ray 532 f then propagatesfurther along the longitudinal axis 521 until it enters the eye of theuser to produce the projected image.

In alternative embodiments to FIG. 5, the quarter-wave retarder layer527 may be located elsewhere within the combiner optic 520, as long asit is between the partial reflectors 526, 528, and still achieve theobjective of reducing or eliminating stray imaging light at point d.

The embodiment of FIG. 6 may be the same as or similar to that of FIG.5, except that another element or elements are added to the distal endof the combiner optic to reduce or eliminate one of the stray rays ofimaging light emerging from that end of the combiner optic.

Many of the constituent parts of the combiner optic 620 may be the sameas or similar to corresponding parts of the optic 520 of FIG. 5. Thus,for example, combiner optic 620 has opposed first and second opticalsurfaces 620 a, 620 b. The optical surface 620 a is at a proximal end ofthe optic 620, suitable for placement near a user's eye. The opticalsurface 620 b is at a distal end of the optic 620. A circumferentialside surface 620 c connects the first and second optical surfaces 620 a,620 b. The combiner optic 620 includes distinct optical bodies (lenses)622, 624, which may be the same as the corresponding bodies of FIG. 5.The combiner optic 620 defines a longitudinal or optical axis 621, whichmay be the same as that of FIG. 5. The combiner optic 620 includes apartial reflector 626 and a partial reflector 628. The partial reflector628 is embedded in the combiner optic 620, sandwiched between theoptical bodies 622, 624, and tilted and curved in such a way that it isnot symmetric with respect to the longitudinal axis 621, and such thatit forms a wedged reflective cavity 629 with the other partial reflector626. The partial reflector 628 may also have a terminus that extendscompletely around the circumferential side surface 620 c, see terminus628 t 1, 628 t 2. At the proximal end of the optic 620, a partialreflector 626 in combination with a retarder layer 627 are attached to,applied to, or formed on the optical surface of the body 622 as shown.The partial reflector 626 and retarder layer 627 may be substantiallythe same as the corresponding elements in FIG. 5; hence, the partialreflector 626 is a linear (broadband or narrow band) reflectivepolarizer, and the retarder layer 627 is a quarter-wave (214) retarder.The partial reflectors 626, 628 and the cavity 629 are designed so thatimaging light of the projected view follows a path from the imagingdevice to the user's eye that includes three reflections in the cavity629. The retarder layer 627 and reflective polarizer (partial reflector)626 are provided to reduce or eliminate a stray beam of imaging lightanalogous to ray 432 d 2 of FIG. 4, in similar fashion to thedescription of FIG. 5.

The rays of imaging light 632, 632 b, 632 c 1, 632 d, 632 e 1, and 632f, as well as imaging light rays 632 c 2, 632 e 2, and 632 g, and thepoints b, c, d, e, f, g, and h, may all correspond substantially totheir respective counterparts in FIG. 5, with no further explanationneeded. The combiner optic 620 of FIG. 6 differs, however, from optic520 by the addition of a film or films at the distal end of the opticwhich absorb one of the circular polarization states of the imaginglight ray. Such film or films is represented in FIG. 6 by absorbinglayer 625. The absorbing layer 625 may be or include, for example, alinear absorbing polarizing film laminated to another quarter-wave (λ/4)retarder film. When properly oriented relative to each other, this filmcombination causes the absorbing layer 625 to absorb imaging light ofone circular polarization state (e.g. CCW) and to transmit imaging lightof the orthogonal circular polarization state (e.g. CW). The transmittedrays 632 c 2, 632 e 2 are of opposite circular polarization states, theformer being CW like ray 632 b, and the latter being CCW like ray 632 d.As such, the absorbing layer 625 can be used to reduce or eliminate oneof the stray beams, such as the one that would otherwise emerge at pointh from ray 632 e 2.

Numerous modifications can be made within the scope of the presentdisclosure, and features and aspects described in connection with oneembodiment will be understood to be applicable also to relatedembodiments. For example, similar to the discussion from FIG. 5, thequarter-wave retarder layer 627 may, in alternative embodiments to FIG.6, be located elsewhere within the combiner optic 620, as long as it isbetween the partial reflectors 626, 628, and still achieve the objectiveof reducing or eliminating stray imaging light at point d. If areflective polarizer is used as a partial reflector in any of thedisclosed embodiments, e.g. as described in connection with FIG. 5 or 6,the reflective polarizer may have a reflectivity for white light in theblock state of polarization of over 99%, of over 90%, of over 70%, orover about 50%. Also, in any cases where a reflective polarizer is usedas a partial reflector, it may be or comprise any suitable reflectivepolarizer, including e.g. a linear reflective polarizer such as abirefringent reflective polarizer, a wire grid reflective polarizer, afiber reflective polarizer, or a disperse reflective polarizer, or acircularly reflective polarizer, such as a cholesteric reflectivepolarizer. Furthermore, the disclosed combiner optics can be used in awide variety of alternative optical imaging systems. In some cases, forexample, the imaging light may include both visible light and invisible(e.g., infrared or ultraviolet) light, while in other cases, the imaginglight may include infrared and/or ultraviolet light but little or novisible light. The detector of the imaging light may be or include ahuman eye as described above, or it may instead be or include anelectronic detector such as a CCD array or other suitable solid statedevice or array of devices, disposed to receive the imaging light thatis reflected by and exits the wedged reflective cavity.

In still other alternative embodiments, each of the disclosed combineroptics can be readily modified such that it no longer functions as acombiner optic, while still retaining the wedged reflective cavity toreflect light that is incident on one side of the optic. This may bedone by replacing one of the partial reflectors with a full reflector,i.e., a reflector whose transmission at the wavelength(s) of interest isnegligible or zero. For example, the partial reflector 528 in FIG. 5 maybe replaced with an identically shaped full reflector (e.g. a muchthicker vapor coat of metal) that has a higher reflectivity and issubstantially opaque at the wavelength(s) of interest. Alternatively orin addition, the modification may be done by incorporating an opaque orsubstantially opaque body, layer, or other element(s) on one side of thewedged reflective cavity. For example, the optical body 524 in FIG. 5may be made of an opaque material, and/or an opaque coating may beapplied to the second optical surface 520 b. In any of these cases, theoptic, as modified, no longer transmits sufficient light at thewavelength(s) of interest to permit detection of remote objects throughthe optic, hence, it is no longer considered to be a combiner optic.Such a modified optic, however, still possesses a wedged reflectivecavity that is configured to redirect light from a source (such assource 330 in FIG. 3A) to a detector (such as the eye 302 in FIG. 3A, ora similarly positioned electronic detector) along an optical path thatincludes three reflections in the wedged reflective cavity, as describedabove. The wedged reflective cavity may of course also include aretarder layer, such as a λ/4 retarder between the two reflectors asdescribed above.

EXAMPLE

The foregoing principles were used to fabricate a combiner opticsuitable for use in near-eye display systems as discussed herein.

In the example, a commercially available plano-convex lens was obtainedas a first optical body. The lens was obtained from Thorlabs, Inc.,Newton, N.J., USA, having product code LA1417. The convex curved opticalsurface of the lens had a 77 mm radius of curvature. A commerciallyavailable plano-concave lens was obtained as a second optical body. Thissecond lens was also obtained from Thorlabs, Inc., Newton, N.J., buthaving product code LC1611. The concave curved optical surface of thislens also had a radius of curvature of about 77 mm, and thus had amating shape relative to the convex shape of the first optical body.

A first partial reflector was formed on the convex optical surface ofthe first optical body. This partial reflector was formed by evaporatingalternating layers of inorganic optical materials on the convex surfaceof the lens to form an inorganic multilayer stack. The multilayer stackhad a total of about 36 layers, and used TiO2 and Al2O3 as the inorganicmaterials. The overall thickness of the multilayer stack was less than 5microns. The thicknesses of its individual layers were such that themultilayer stack functioned as a notched reflector, with a reflectivityas shown as curve 710 in FIG. 7. The reflectivity of FIG. 7 was measuredon a spectrophotometer using unpolarized light at normal incidence tothe stack. The normal incidence reflectivity of the multilayer stack wassubstantially polarization insensitive. As seen in the curve 710, thenotched reflector produced by the multilayer stack had three distinctreflection bands: a band 710 a which peaked at 450 nm (blue light), aband 710 b which peaked at 547 nm (green light), and a band 710 c whichpeaked at 624 nm (red light).

The first partial reflector (the inorganic multilayer stack) was thensandwiched between the first and second optical bodies by bonding theexposed side of the multilayer stack to the concave optical surface ofthe second optical body using a UV curable adhesive.

A linear reflective polarizing film was then obtained for use as asecond partial reflector. The reflective polarizing film used wasproduct code APF, available from 3M Company, St. Paul, Minn., which is apolymeric multilayer optical film. Before applying this film to theplanar optical surface of the plano-convex lens, a quarter-wave retarderfilm was applied and bonded to that surface using an optically clearadhesive, product code OCA available from 3M Company, St. Paul, Minn.The reflective polarizing film was then applied and bonded to theretarder film using the same optically clear adhesive, such that thepass axis of the reflective polarizer was at a 45 degree angle to thefast axis of the retarder film. (The block axis of the reflectivepolarizer was thus also at a 45 degree angle to the fast axis of theretarder film.) After this, the lens combination was cut in half axiallyto produce two combiner optics having mirror symmetry relative to eachother.

One of the resulting combiner optics is pictured in FIGS. 8 and 9. InFIG. 8, the combiner optic is shown resting on a printed surface in aroom lit by ambient office lights. In this photograph, the (planar)reflective polarizer side of the optic faces the viewer, and bothtransmitted and reflected images of the nearby text can be seen. FIG. 9is a photograph that shows the combiner optic producing a reflected(real) image. The output of a monochrometer was directed through a 10 mmby 1 mm aperture, and then through an absorbing polarizer. The aperturecan be seen to be imaged onto a plane near the lens in reflection.

Unless otherwise indicated, all numbers expressing quantities,measurement of properties, and so forth used in the specification andclaims are to be understood as being modified by the term “about”.Accordingly, unless indicated to the contrary, the numerical parametersset forth in the specification and claims are approximations that canvary depending on the desired properties sought to be obtained by thoseskilled in the art utilizing the teachings of the present application.Not as an attempt to limit the application of the doctrine ofequivalents to the scope of the claims, each numerical parameter shouldat least be construed in light of the number of reported significantdigits and by applying ordinary rounding techniques. Notwithstandingthat the numerical ranges and parameters setting forth the broad scopeof the invention are approximations, to the extent any numerical valuesare set forth in specific examples described herein, they are reportedas precisely as reasonably possible. Any numerical value, however, maywell contain errors associated with testing or measurement limitations.

Various modifications and alterations of this invention will be apparentto those skilled in the art without departing from the spirit and scopeof this invention, and it should be understood that this invention isnot limited to the illustrative embodiments set forth herein. The readershould assume that features of one disclosed embodiment can also beapplied to all other disclosed embodiments unless otherwise indicated.All U.S. patents, patent application publications, and other patent andnon-patent documents referred to herein are incorporated by reference,to the extent they do not contradict the foregoing disclosure.

The invention claimed is:
 1. A near-eye display system to permitsimultaneous viewing of remote objects and a projected image, the systemcomprising: a combiner optic having a proximal end and a distal end, theproximal end being suitable for placement near a user's eye; and animaging device disposed to direct imaging light towards the proximal endof the combiner optic; wherein the combiner optic includes first andsecond partial reflectors that form a wedged reflective cavity, theimaging light following a light path to the user's eye that includesthree reflections in the wedged reflective cavity, wherein the firstpartial reflector is a circular reflective polarizer.
 2. A near-eyedisplay system to permit simultaneous viewing of remote objects and aprojected image, the system comprising: a combiner optic having aproximal end and a distal end, the proximal end being suitable forplacement near a user's eye; and an imaging device disposed to directimaging light towards the proximal end of the combiner optic; whereinthe combiner optic includes first and second partial reflectors thatform a wedged reflective cavity, the imaging light following a lightpath to the user's eye that includes three reflections in the wedgedreflective cavity, wherein the first partial reflector is a linearreflective polarizer, and the combiner optic further includes a retarderlayer disposed between the first and second partial reflectors.
 3. Thesystem of claim 2, wherein the retarder layer has a retardance ofsubstantially λ/4.
 4. The system of claim 2, wherein the threereflections in the reflective cavity include a first reflection at thereflective polarizer and a first and second reflection at the secondpartial reflector.
 5. The system of claim 4, wherein the retarder layerhas a fast axis and the reflective polarizer has a pass axis, and thefast axis is oriented relative to the pass axis so that the firstreflection at the reflective polarizer occurs with little or notransmission of the imaging light through the reflective polarizer.
 6. Anear-eye display system to permit simultaneous viewing of remote objectsand a projected image, the system comprising: a combiner optic having aproximal end and a distal end, the proximal end being suitable forplacement near a user's eye, and an imaging device disposed to directimaging light towards the proximal end of the combiner optic, whereinthe combiner optic includes first and second partial reflectors thatform a wedged reflective cavity, the imaging light following a lightpath to the user's eye that includes three reflections in the wedgedreflective cavity, wherein the combiner optic includes distinct firstand second lenses, and the first lens attaches to the second lensthrough the second partial reflector.
 7. The system of claim 6, whereinthe first lens has a first curved surface, and the second lens has asecond curved surface shaped to match the first curved surface.
 8. Anear-eye display system to permit simultaneous viewing of remote objectsand a projected image, the system comprising: a combiner optic having aproximal end and a distal end, the proximal end being suitable forplacement near a user's eye; and an imaging device disposed to directimaging light towards the proximal end of the combiner optic; whereinthe combiner optic includes first and second partial reflectors thatform a wedged reflective cavity, the imaging light following a lightpath to the user's eye that includes three reflections in the wedgedreflective cavity, wherein the second partial reflector is a notchedreflector.
 9. The system of claim 8, wherein, over a wavelength rangefrom 400-700 nm, the notched reflector includes at least one distinctreflection band whose full width at half maximum (FWHM) is less than 100nanometers.
 10. A near-eye display system to permit simultaneous viewingof remote objects and a projected image, the system comprising: acombiner optic having a proximal end and a distal end, the proximal endbeing suitable for placement near a user's eye, and an imaging devicedisposed to direct imaging light towards the proximal end of thecombiner optic, wherein the combiner optic includes first and secondpartial reflectors that form a wedged reflective cavity, the imaginglight following a light path to the user's eye that includes threereflections in the wedged reflective cavity, wherein the second partialreflector has a reflectivity at normal incidence that is substantiallyinsensitive to polarization state.
 11. A near-eye display system topermit simultaneous viewing of remote objects and a projected image, thesystem comprising: a combiner optic having a proximal end and a distalend, the proximal end being suitable for placement near a user's eye;and an imaging device disposed to direct imaging light towards theproximal end of the combiner optic; wherein the combiner optic includesfirst and second partial reflectors that form a wedged reflectivecavity, the imaging light following a light path to the user's eye thatincludes three reflections in the wedged reflective cavity, wherein,over a wavelength range from 400-700 nm, the second partial reflectorhas no distinct reflection band whose full width at half maximum (FWHM)is less than 100 nanometers.
 12. A near-eye display system to permitsimultaneous viewing of remote objects and a projected image, the systemcomprising: a combiner optic having a proximal end and a distal end, theproximal end being suitable for placement near a user's eye; and animaging device disposed to direct imaging light towards the proximal endof the combiner optic; wherein the combiner optic includes first andsecond partial reflectors that form a wedged reflective cavity, theimaging light following a light path to the user's eye that includesthree reflections in the wedged reflective cavity, wherein the firstpartial reflector has an average reflectivity for the imaging light in arange from 25% to 75%.
 13. The system of claim 12, wherein the firstpartial reflector is a reflective polarizer.
 14. The system of claim 12,wherein the first partial reflector is disposed at or near the proximalend of the combiner optic, such that the imaging light propagating alongthe light path encounters the first partial reflector beforeencountering the second partial reflector.
 15. A near-eye display systemto permit simultaneous viewing of remote objects and a projected image,the system comprising: a combiner optic having a proximal end and adistal end, the proximal end being suitable for placement near a user'seye; and an imaging device disposed to direct imaging light towards theproximal end of the combiner optic; wherein the combiner optic includesfirst and second partial reflectors that form a wedged reflectivecavity, the imaging light following a light path to the user's eye thatincludes three reflections in the wedged reflective cavity, wherein thesecond partial reflector has an average reflectivity for the imaginglight in a range from 25% to 75%.
 16. A near-eye display system topermit simultaneous viewing of remote objects and a projected image, thesystem comprising: a combiner optic having a proximal end and a distalend, the proximal end being suitable for placement near a user's eye;and an imaging device disposed to direct imaging light towards theproximal end of the combiner optic; wherein the combiner optic includesfirst and second partial reflectors that form a wedged reflectivecavity, the imaging light following a light path to the user's eye thatincludes three reflections in the wedged reflective cavity, wherein thefirst partial reflector is a reflective polarizer, and wherein thereflective polarizer defines a pass state and a block state ofpolarization, and the block state of the reflective polarizer provides anotched reflection spectrum, and the imaging light comprises one or moredistinct spectral output peaks corresponding to the notched reflectionspectrum.
 17. The system of claim 16, wherein the second partialreflector is a notched reflector having a second notched reflectionspectrum corresponding to the notched reflection spectrum of the blockstate of the reflective polarizer.
 18. A combiner optic having aproximal end and a distal end, the combiner optic conprising: a firstlens at or near the proximal end; a second lens at or near the distalend, and first and second partial reflectors disposed on opposed ends ofthe first lens, the first partial reflector being attached to a firstsurface of the first lens, and the second partial reflector beingsandwiched between the first and second lenses; wherein the first andsecond partial reflectors have sufficient light transmission to permitviewing of remote objects through the combiner optic, and wherein thefirst and second partial reflectors form a wedged reflective cavity,wherein the first partial reflector is a linear reflective polarizer,and wherein the combiner optic further comprises a retarder layerdisposed between the first and second partial reflectors.
 19. A combineroptic having a proximal end and a distal end, the combiner opticcomprising: a first lens at or near the proximal end; a second lens ator near the distal end; and first and second partial reflectors disposedon opposed ends of the first lens, the first partial reflector beingattached to a first surface of the first lens, and the second partialreflector being sandwiched between the first and second lenses; whereinthe first and second partial reflectors have sufficient lighttransmission to permit viewing of remote objects through the combineroptic, and wherein the first and second partial reflectors form a wedgedreflective cavity, wherein reflectivities of the first and secondpartial reflectors are tailored such that imaging light directed at theproximal end provides a viewable image to an eye disposed near theproximal end via a light path that includes three reflections in thewedged reflective cavity.
 20. The combiner optic of claim 19, whereinthe first partial reflector is a reflective polarizer.
 21. An optic thatredirects light from a source to a detector, the optic comprising areflective polarizer and a reflector, the reflective polarizer and thereflector forming a wedged reflective cavity, the optic furthercomprising a retarder layer between the reflective polarizer and thereflector, the retarder layer being oriented relative to the reflectivepolarizer such that light that enters the wedged reflective cavitythrough the reflective polarizer exits the wedged reflective cavitythrough the reflective polarizer after three reflections in the wedgedreflective cavity, wherein the reflective polarizer is a notchedreflector.
 22. An optic that redirects light from a source to adetector, the optic comprising a reflective polarizer and a reflector,the reflective polarizer and the reflector forming a wedged reflectivecavity, the optic further comprising a retarder layer between thereflective polarizer and the reflector, the retarder layer beingoriented relative to the reflective polarizer such that light thatenters the wedged reflective cavity through the reflective polarizerexits the wedged reflective cavity through the reflective polarizerafter three reflections in the wedged reflective cavity, wherein theoptic has insufficient light transmission to permit optical detection ofremote objects through the wedged reflective cavity or through theoptic, such that the optic is not a combiner optic.
 23. The optic ofclaim 22, wherein the reflective polarizer is a broad band polarizerthat operates over most or all of a visible wavelength spectrum.
 24. Theoptic of claim 22, wherein the reflective polarizer has a reflectivityfor at least some light in a block state of polarization of over 50%.25. The optic of claim 22, wherein the retarder layer has a retardanceof substantially λ/4.
 26. The optic of claim 22, wherein the reflectoris a partial reflector with sufficient light transmission to permitoptical detection of remote objects through the wedged reflective cavityand through the optic, such that the optic is a combiner optic.
 27. Asystem comprising the optic of claim 22 in combination with an imagingdevice that directs imaging light towards the reflective polarizer ofthe optic.
 28. A system comprising the optic of claim 22 in combinationwith a detector disposed to receive the light that exits the wedgedreflective cavity through the reflective polarizer.